Grains of a solar ingot polysilicon wafer are generally sized at about 1 cm, and the number of grains of a single silicon wafer is more than 500. The grains are different due to their crystal orientations, and also have different effects on the subsequence battery processes. For example, a <100> crystal orientation may obtain, by alkali texturization, a pyramid textured surface with a high light-harvesting effect, while a <111> crystal orientation can obtain a textured surface only through acid texturization or other isotropic texturization ways. Different grains have different crystal orientations and different crystal orientations have different textured surface properties, which in turn result in different surface recombination rates, affecting performance parameters of the final battery. As such, proper detection and evaluation of the crystal orientations of the entire silicon wafer facilitates optimization of a fabricating process of the battery. However, depending on the current technology level, an effect of properly measuring the crystal orientations of the entire silicon wafer has not been achieved yet.
Currently, there are three major types of methods for measuring the crystal orientations:
1) X-ray diffraction (briefly referred to as XRD) technology, wherein its beam spot generally has a diameter of several millimeters (mm) and each time only a crystal orientation of a single grain of the silicon wafer can be measured. This is high in cost and very time consuming, and cannot fully satisfy requirements of the industry.
2) Electron backscattered selective diffraction (briefly referred to as EBSD) technology, which is suitable for detecting crystal orientation of a microdomain and may be used for surface scanning, wherein its spatial resolution may be up to 0.1 μm, but the range being measured is also limited to only several square centimeters (cm2), not suitable for quickly characterizing a full-size silicon wafer.
3) A rotating table reflection approach (CN103151283A, the entirety of which is incorporated into the present application by reference and acts as a part of the disclosure of the specification), which was proposed previously by the inventors of the present application. This technical solution can achieve crystal orientation calculation on a large-area sample. The rotating table reflection approach disclosed by CN103151283A has already possessed efficient industrial practicality. However, during its implementation, the applicant has further found the following aspect to be improved: its calculation method is a method to make comparison with a standard crystal orientation, which has a limited theoretical accuracy.
In view of the state of the art, there exists an urgent requirement in the current photovoltaic field to provide a technology for detecting the crystal orientation of the silicon wafer more quickly and accurately.